Sparse Autoencoder in theano

Last month I was reading about Autoencoders for Collaborative filtering. Using Autoencoders for Collaborative filtering is a fairly recent idea and it proven to be very effective beating all state-of-art SVD based methods. Actually the idea is pretty simple, instead of using linear function for Matrix Factorization (dot product of the two latent factor matrices, use some complex non-linear function of the two matrices so as to capture more complicated dependencies. Autoencoders are a way to do so. Matrix Factorization based CF minimizes the following objective: Note that in the objective function only known/observed user-rating pairs (set O) are considered.